On Fri, Mar 28, 2025 at 02:57:41PM +0200, Elena Reshetova wrote: > SGX architecture introduced a new instruction called EUPDATESVN > to Ice Lake. It allows updating security SVN version, given that EPC > is completely empty. The latter is required for security reasons > in order to reason that enclave security posture is as secure as the > security SVN version of the TCB that created it. > > Additionally it is important to ensure that while ENCLS[EUPDATESVN] > runs, no concurrent page creation happens in EPC, because it might > result in #GP delivered to the creator. Legacy SW might not be prepared > to handle such unexpected #GPs and therefore this patch introduces > a locking mechanism to ensure no concurrent EPC allocations can happen. > > It is also ensured that ENCLS[EUPDATESVN] is not called when running > in a VM since it does not have a meaning in this context (microcode > updates application is limited to the host OS) and will create > unnecessary load. > > This patch is based on previous submision by Cathy Zhang > https://lore.kernel.org/all/20220520103904.1216-1-cathy.zh...@intel.com/ > > Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> > --- > arch/x86/include/asm/sgx.h | 41 +++++++++++++-------- > arch/x86/kernel/cpu/sgx/encls.h | 6 ++++ > arch/x86/kernel/cpu/sgx/main.c | 63 ++++++++++++++++++++++++++++++++- > arch/x86/kernel/cpu/sgx/sgx.h | 1 + > 4 files changed, 95 insertions(+), 16 deletions(-) > > diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h > index 6a0069761508..5caf5c31ebc6 100644 > --- a/arch/x86/include/asm/sgx.h > +++ b/arch/x86/include/asm/sgx.h > @@ -26,23 +26,26 @@ > #define SGX_CPUID_EPC_SECTION 0x1 > /* The bitmask for the EPC section type. */ > #define SGX_CPUID_EPC_MASK GENMASK(3, 0) > +/* EUPDATESVN presence indication */ > +#define SGX_CPUID_EUPDATESVN BIT(10) > > enum sgx_encls_function { > - ECREATE = 0x00, > - EADD = 0x01, > - EINIT = 0x02, > - EREMOVE = 0x03, > - EDGBRD = 0x04, > - EDGBWR = 0x05, > - EEXTEND = 0x06, > - ELDU = 0x08, > - EBLOCK = 0x09, > - EPA = 0x0A, > - EWB = 0x0B, > - ETRACK = 0x0C, > - EAUG = 0x0D, > - EMODPR = 0x0E, > - EMODT = 0x0F, > + ECREATE = 0x00, > + EADD = 0x01, > + EINIT = 0x02, > + EREMOVE = 0x03, > + EDGBRD = 0x04, > + EDGBWR = 0x05, > + EEXTEND = 0x06, > + ELDU = 0x08, > + EBLOCK = 0x09, > + EPA = 0x0A, > + EWB = 0x0B, > + ETRACK = 0x0C, > + EAUG = 0x0D, > + EMODPR = 0x0E, > + EMODT = 0x0F, > + EUPDATESVN = 0x18, > }; > > /** > @@ -73,6 +76,11 @@ enum sgx_encls_function { > * public key does not match IA32_SGXLEPUBKEYHASH. > * %SGX_PAGE_NOT_MODIFIABLE: The EPC page cannot be modified because it > * is in the PENDING or MODIFIED state. > + * %SGX_INSUFFICIENT_ENTROPY: Insufficient entropy in RNG. > + * %SGX_EPC_NOT_READY: EPC is not ready for SVN update. > + * %SGX_NO_UPDATE: EUPDATESVN was successful, but CPUSVN was not > + * updated because current SVN was not newer than > + * CPUSVN. > * %SGX_UNMASKED_EVENT: An unmasked event, e.g. INTR, was > received > */ > enum sgx_return_code { > @@ -81,6 +89,9 @@ enum sgx_return_code { > SGX_CHILD_PRESENT = 13, > SGX_INVALID_EINITTOKEN = 16, > SGX_PAGE_NOT_MODIFIABLE = 20, > + SGX_INSUFFICIENT_ENTROPY = 29, > + SGX_EPC_NOT_READY = 30, > + SGX_NO_UPDATE = 31, > SGX_UNMASKED_EVENT = 128, > }; > > diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h > index 99004b02e2ed..3d83c76dc91f 100644 > --- a/arch/x86/kernel/cpu/sgx/encls.h > +++ b/arch/x86/kernel/cpu/sgx/encls.h > @@ -233,4 +233,10 @@ static inline int __eaug(struct sgx_pageinfo *pginfo, > void *addr) > return __encls_2(EAUG, pginfo, addr); > } > > +/* Update CPUSVN at runtime. */ > +static inline int __eupdatesvn(void) > +{ > + return __encls_ret_1(EUPDATESVN, ""); > +} > + > #endif /* _X86_ENCLS_H */ > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c > index b61d3bad0446..24563110811d 100644 > --- a/arch/x86/kernel/cpu/sgx/main.c > +++ b/arch/x86/kernel/cpu/sgx/main.c > @@ -32,6 +32,11 @@ static DEFINE_XARRAY(sgx_epc_address_space); > static LIST_HEAD(sgx_active_page_list); > static DEFINE_SPINLOCK(sgx_reclaimer_lock); > > +/* This lock is held to prevent new EPC pages from being created > + * during the execution of ENCLS[EUPDATESVN]. > + */ > +static DEFINE_SPINLOCK(sgx_epc_eupdatesvn_lock); > + > static atomic_long_t sgx_nr_used_pages = ATOMIC_LONG_INIT(0); > static unsigned long sgx_nr_total_pages; > > @@ -457,7 +462,17 @@ static struct sgx_epc_page > *__sgx_alloc_epc_page_from_node(int nid) > page->flags = 0; > > spin_unlock(&node->lock); > - atomic_long_inc(&sgx_nr_used_pages); > + > + if (!atomic_long_inc_not_zero(&sgx_nr_used_pages)) { > + spin_lock(&sgx_epc_eupdatesvn_lock); > + /* Only call sgx_updatesvn() once the first enclave's > + * page is allocated from EPC > + */ > + if (atomic_long_read(&sgx_nr_used_pages) == 0) > + sgx_updatesvn(); > + atomic_long_inc(&sgx_nr_used_pages); > + spin_unlock(&sgx_epc_eupdatesvn_lock); > + } > > return page; > } > @@ -970,3 +985,49 @@ static int __init sgx_init(void) > } > > device_initcall(sgx_init); > + > +/** > + * sgx_updatesvn() - Issue ENCLS[EUPDATESVN] > + * If EPC is ready, this instruction will update CPUSVN to the currently > + * loaded microcode update SVN and generate new cryptographic assets. > + */ > +void sgx_updatesvn(void) > +{ > + int retry = 10; > + int ret; > + > + lockdep_assert_held(&sgx_epc_eupdatesvn_lock); > + > + if (!(cpuid_eax(SGX_CPUID) & SGX_CPUID_EUPDATESVN)) > + return; > + > + /* Do not execute ENCLS[EUPDATESVN] if running in a VM since > + * microcode updates are only meaningful to be applied on the host. > + */ > + if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) > + return; > + > + do { > + ret = __eupdatesvn(); > + if (ret != SGX_INSUFFICIENT_ENTROPY) > + break; > + > + } while (--retry); > + > + switch (ret) { > + case 0: > + pr_info("EUPDATESVN: success\n"); > + break; > + case SGX_EPC_NOT_READY: > + case SGX_INSUFFICIENT_ENTROPY: > + case SGX_EPC_PAGE_CONFLICT: > + pr_err("EUPDATESVN: error %d\n", ret); > + break; > + case SGX_NO_UPDATE: > + break; > + default: > + pr_err("EUPDATESVN: unknown error %d\n", ret); > + break; > + }
Overall, I think you're right in that "inversion" does make sense, now that other stuff is better aligned. At least when there is spurious error, I think ioctl's should stop responding and driver should not do anything useful anymore. I.e., it should go out-of-service. I don't think the driver should tear-down, just stop servicing VM's and responding ioctl's. Possibly thish should be also right action for other errors than "insufficient entropy" but I'm open for comments for this. BR, Jarkko
